A former government scientist charged with attempting to sell technology secrets to Israel has confessed to one count of attempted espionage.
Stewart Nozette is expected to serve a sentence of 13 years in prison after making a plea deal with prosecutors.
He has been in jail since his arrest in 2009 after a sting operation by an undercover FBI agent posing as an Israeli intelligence officer.
Nozette, 54, was accused of seeking millions of dollars to sell secrets.
He could have faced a death sentence if convicted on all four counts of attempted espionage with which he had been charged.
The Department of Justice said none of the charges alleged that any US laws were broken by the government of Israel or anyone working on its behalf.
Nozette had high-level security clearances during several decades of working for the government, including at Nasa, the National Space Council and the Department of Energy.
He appeared on Wednesday in court in a prison jumpsuit and told the judge he understood the charge to which he was pleading.
Nozette told the undercover FBI agent - who posed as an officer for the Israeli secret service, Mossad - that the secrets he was offering had cost the US government anywhere from $200m (£125m) to nearly $1bn to develop.
According to court papers, Nozette met the undercover agent at the upmarket Mayflower Hotel in downtown Washington in October 2009.
He is quoted as telling the agent: "I've crossed the Rubicon... I've made a career choice."
"I'm prepared to give them the whole thing... all the technical specifications," he is also quoted as having said.
Out of his suburban Washington home, Nozette ran the Alliance for Competitive Technology, a non-profit organisation with agreements to develop technology for the US government.
Prosecutors say Nozette agreed to provide regular information to Mossad through a post office box in exchange for money.
He allegedly asked for an Israeli passport and accepted two payments - both under $10,000, so as to avoid reporting them.
In return for the money, Nozette allegedly agreed to divulge information about US satellites, early warning systems and major elements of defence strategy.
"Stewart Nozette betrayed America's trust by attempting to sell some of the nation's most closely guarded secrets for profit," Lisa Monaco, assistant attorney general in charge of the justice department's national security division, told Reuters news agency.
Attorney General Eric Holder has ordered special communications restrictions placed on Nozette in jail.
The former scientist's top-secret knowledge reportedly covers America's nuclear missile programme.
US Attorney Ronald Machen said in a statement: "Today [Nozette] is a disgraced criminal who was caught red-handed attempting to trade American secrets for personal profit.
"He will now have the next 13 years behind bars to contemplate his betrayal."
District Judge Paul Friedman said he was prepared to accept the plea deal, provided Nozette co-operated with prosecutors. He set the next hearing in the case for 15 November.